This invention relates to a donor roll with electrically insulated journals.
Electrostatic reproduction and printing involves uniformly charging a photoconductive member, or photoreceptor, and imagewise discharging it, or imagewise exposing it, based on light reflected from, or otherwise representing, an original image being reproduced or printed. The result is an electrostatically-formed latent image on the photoconductive member. The latent image is developed by bringing a charged developer material into contact with the photoconductive member to form a toner powder image. The toner powder image is transferred to a receiving sheet and then fused by heating.
This process can be modified to form color images. One type of process, called image-on-image processing, superimposes toner powder images of different color toners onto the toner prior to the transfer of the composite toner powder image onto the substrate.
Two-component and single-component developer materials are known. Two-component developer materials comprise magnetic carrier particles and charged toner particles that adhere triboelectrically to the carrier particles and are intended to adhere the photoconductive member.
Single-component developer material typically include only toner particles. The toner particles typically have an electrostatic charge to adhere to the photoconductive member, and magnetic properties to magnetically convey the toner particles from the sump to the developer roll. The toner particles adhere directly to the developer roll. The toner particles are attracted to the donor roll from a magnet or developer roll. From the donor roll, the toner is transferred to the photoconductive member in the development zone.
For both types of developer material, the charged toner particles are brought into contact with the latent image to form a toner image on the photoconductive member. The toner image is transferred to a receiver sheet, which passes through a fuser device where the toner particles are heated and permanently fused to the sheet, forming a hard copy of the original image.
A development device is used to bring the charged toner particles into contact with the latent image formed on the photoreceptor, so that the toner particles adhere electrostatically to the charged areas on the latent image. The development device typically includes a chamber in which the developer material is mixed and charged.
One type of two-component development method and apparatus is known as xe2x80x9cscavengeless developmentxe2x80x9d. xe2x80x9cHybridxe2x80x9d scavengeless development apparatus typically include a mixing chamber that holds a two-component developer material, at least one developer material developer or magnetic roll, a donor roll, a development zone, and an electrode structure at the development zone between the donor roll and the photoconductive member. The donor roll receives charged toner particles from the developer roll and transports the particles to the development zone. An AC voltage is applied to the electrodes to form a toner cloud in the development zone. Electrostatic fields generated by an adjacent latent image on the photoconductive member surface attract charged toner particles from the toner cloud to develop the latent image on the photoconductive member.
Another variation on scavengeless development uses single-component developer material development systems. As in two-component developer material development systems, the donor roll and electrodes also create a toner cloud.
In both one-component and two-component developer scavengeless development systems, the development apparatus should be able to effectively and controllably transport toner particles into the development zone and donate the charged toner particles to the photoconductive member, to achieve high-quality image development.
In scavengeless development systems, an important factor in achieving effective and controllable transfer of charged toner particles from the donor roll to the photoconductive member is the dimensional control of the components that are involved in the transfer function. The macrouniformity is the result of the accumulated tolerance of these components. Typically, the components include the donor roll, the photoconductive member, such as a photoreceptor belt, and a backerbar that contacts the photoreceptor belt""s inner surface opposite to the outer surface to which the toner is transferred.
For proper operation of the donor roll in a hybrid scavengeless development system, the diameter tolerance, runout and surface finish of the donor roll should be as precise as possible. Donor rolls are typically formed by machining a cylindrical body from solid cylindrical stock material, and forming a bore in each of the opposed end faces of the body. Journals are formed from smaller cylindrical stock material and fitted into the bores at both ends of the body. The journals are mounted to bearings to allow for rotation of the roll.
The outer peripheral surface of the body should have a precision size, roundness and runout requirements with respect to the journals. As the roll is rotated about the journals, the outer periphery of the roll may have an eccentric pattern or runout with respect to the journals. The total runout of the donor roll includes the runout between the periphery of the body and counterbore inside diameter, the roundness of the body, and the roundness of the journals.
In addition to the tolerances of the donor roll, the tolerances of the backerbar, photoconductive member and other components involved in the transfer of toner from the donor roll to the photoconductive member contribute to the macrouniformity in the development zone.
If the development zone of the development apparatus changes excessively during imaging due to poor dimensional control of the components, then the ability of the apparatus to effectively and controllably donate charged toner particles to the photoconductive member and achieve high-quality image development can be adversely affected. Particularly, if the total allowable deviations or the development zone nonuniformity of the components involved in the transfer of the charged toner particles from the donor roll to the photoconductive member is too high such that gap non-uniformity occurs then toner may conceivably not deposit uniformly.
The above tolerance requirements are exacerbated in a development system where the donor roll and backerbar need to be spaced closely and electrically isolated from each other. The prior mentioned macrouniformity specification which is a result of the dimensional accuracy of the donor roll and backerbar among others, is gauged when the one bearing on the inboard end and one on the out board end of the donor roll docks onto the top of the radius of the backerbar. The bearings outer diameter is larger than the roll body outer diameter thus when docked, keeping the body a set distance from the backerbar. It is in this gap the photoreceptor is passed. Toner from the donor roll is transferred to the PR belt at the backerbars location. At this point there is a latent image on the belt ready to be developed. As the belt moves by various toners, the toner moves off of the roll to the belt. This requires the toner be of one charge (+) and the image be another (xe2x88x92). Electrically insulating the donor roll bearings from the backerbars prevents electric charges from being transferred from the donor roll, through the backerbars to the photoreceptor belt thus neutralizing the latent image.
There is provided a donor structure for developing toner images to an image receiving surface, said structure comprising: a core structure; end caps including journal portions attached to said core structure; a bearing for operatively supporting said donor structure in an imaging device; and electrically isolating coatings carried by said journal portions, said electrically isolating coatings being interposed between said journal portions and said bearings.